Control systems for cranes

ABSTRACT

A control system for an electric crane or hoist motor supplied through thyristor circuitry wherein the lifting and lowering speed and travel is controlled by saw tooth voltage generators which adjust the firing angle of the thyristors, the sawtooth waveform being applied to the trigger electrodes of the thyristors.

United States Patent Inventor Anthony Walter Davey Long Whatton,Hathern, England Appl. No. 744,961 Filed July 15, 1968 Patented July 27,1971 Assignee Herbert Morrk Limited Loughborough, England Priority July21, 1967 Great Britain 33622/67 CONTROL SYSTEMS FOR CRANES 5 Claims, 8Drawing Figs.

US. Cl. 318/203, 318/258, 318/289 Int. Cl. H02p 1/40 Field of Search318/202, 203, 258, 289

[56] References Cited UNITED STATES PATENTS 2,823,34l 2/1958 Smith et al318/203 3,248,625 4/1966 Wycofi' 318/203 3,402,335 9/1968 Smith et al318/202 3,430,122 2/ 1969 Krabbe et al. 318/203 Primary Examiner0ris L.Rader Assistant Examiner-Gene Z Rubinson Attorney-Norris and BatemanABSTRACT: A control system for an electric crane or hoist motor suppliedthrough thyristor circuitry wherein the lifting and lowering speed andtravel is controlled by saw tooth voltage generators which adjust thefiring angle of the thyristors, the sawtooth waveform being applied tothe trigger electrodes of the thyristors. t

PATENTEDJUL27 197i SHEET 2 OF 6 .M 5 m M CW R 0 P E M K 1 6 T qqw oo 05% c J Macon. ui D 4/. M I E M m a w ACTO IN VE N TOP ANTHONY WALTERDAVEY W ,2 Mam Attys PATENTED JUL27 I97| 3 596, 156

SHEET 3 UF 6 INVENTOP ANTHONY WALTER DAVEY Attys PATENTEI] JUL27|971596, l 56 SHEET 5 0F 6 INVENTOP ANTHONY WALTER DAVEY Attys.

PATENTEU m2 1 m1 SHEET 6 [1F 6 vvvv AIAAA lllll Y rvvvvv PL IC NVE/V TOPANTHONY WALTER DAVEY Attys CONTROL SYSTEMS FOR CRANES This inventionrelates to improvements in control systems for cranes and hoists."

According to the. invention a control system for cranes or hoistscomprising thyristor circuitry employing sawtooth voltage waveform forcontrolling the lifting and lowering speed of cranes and hoists.

The invention will be described with reference to the accompanyingdrawings:

FIG. 1 is a diagrammatic view of one form of the invention,

- FIGS. 2A, 2B, 2C show a circuit diagram for the form of the inventionshown diagrammatically in FIG. 1, FIGS. 23 and 2C are continuations of2A;

FIG. 3 is a diagrammatic view of a further arrangement;

FIGS. 4A and 4B show a circuit diagram of themodified arrangement of theinvention shown diagrammatically in FIG. 3. FIG. 4B is a continuation ofFIG. 4A;

FIG. 5 is a detail diagram of part of the circuit of the controller RCshown in FIG. 3.

, When using a slip ring or squirrel cage motor F (FIG. I) the supply isfed through fuses a to reversing contactors A and B which may be staticswitches. The contactors, A, B are controlled by the driver by operationof the controller RC, which may be replaced by relays if remote controlis required.

The operation of the contactors A or B by the controller C also operatesa brake D, which is of the electromagnetic type.

The voltage from the contactors is also applied to a static control unitE the diagram of which is shown in FIGS. 2A- 2C.

The controlled voltage from the static control unit E is then fed to themotor F, which may be a squirrel cage or slip ring motor. The motor Fdrives a tachogenerator G to provide feedback to the control unit B.

When a slip ring motor is used (FIG. l).the motor resistance isshort-circuited by contactor contacts J, K and L. The contactors J, K, Lare controlled through a tachogenerator G and the control unit E so thatthey operate at the correct motor speed to give optimum torque over thespeed range.

The complete control circuit for a hoist is shown in FIG. 2A-20. I

The speed is controlled by varying the voltage to the motor by means ofthyristors D1, D4 and D7. The thyristors are series elements in themotor supply leads, terminals P and A, Q and B, R and C being providedfor each of the supply phases as shown in FIG. 2A for lifting andlowering. The travel control is shown in FIG. 4A by diodes D1 and D2,D11 and D12, D21 and D22 and their associatedcapacitors C1, C and C16.

The return current from the motor passes through rectifiers D2, D5 andD8; surge suppressors D3, D6 and D9 conduct when surge voltages arepresent to clip the voltage and protect the thyristors.

For hoisting, full power is initially applied to the motor by operationof controller RC contact RC/I-ll, for first speed and RC/l-IZ forsecond, etc., to ensure that the load always hoists, and onreaching theset speed, the firing angle of the thyristors iscontrolled so that themotor power is reduced sufficiently to maintain that speed. C

Any deviation of speed will cause a corresponding change of motor powerto correct the change of speed.

For lowering moderate to heavy loads the motor is connected as forhoisting and, when the controller RC is operated, the hoist contactor Ais energized and the brake D will release. The firing angle of thethyristors is such that no power will be applied to the motor and theload will accelerate down under gravity. At the set lowering speed thethyristor firing angle will change and apply sufficient braking power tomaintain that speed.

For light loads, when the brake D is released the load will not descend.A circuit comprising transistor TRIO, relay RL3, transistor TR11, TR22,relay RL4 and their associated components will, after a short delay andno tachogenerator output,

ing relay RL3 to reverse the motor torque by means of its contact RL3Adeenergizing contactor A and energizingcontactor B, connecting the motorF in the lowering direction.

Contacts R3L/C and R3L/D reverse the polarity of the tachogeneratorinduced voltage such that the polarity of the signal applied totransistor TR13 and TRl5 FIG.- 2B is as for hoisting and a reduction. inmotor power when the set speed is reached takes place similarly to thatfor hoisting.

Contact RL3/B prevents contact Rl4/A discharging capacitor C19 oncecontact RL3/B also short circuits resistor R to 7 ensure that thethyristors are initially turned full on.

ResistorR47 and diode D35 ensure a quick discharge of C19 when thecontroller RC is returned to the off position via terminal 28 nowreconnected to terminal 35 (earth).

Should there be a load on the hook, the load will descend under gravitywhen the brake is released. The tachogenerator G which is coupled to themotor will turn and produce a voltage which will cause transistor TR11to conduct and hence transistor TR22. Transistor TR22 will energizerelay RL4 which will discharge capacitor C19 by means of contact RL4Apreventing R13 from operating.

The base of transistor TR11 is connected to one tachogeneratorconnection via resistors R52 and R51, the emitter of transistor TR11 isconnected to the other tachogenerator connection via relay contactRL3/C, when the tachogenerator starts to turn the small voltagegenerated causing the transistor to conduct.

Zener diode D55 clips the voltage to prevent damage to transistor TR11when the tachogenerator is running at fast speed the resistor R51 actsas the ballast resistor. Resistor R52 limits the base current of TR11 atfast speed when the full Zener voltage is present'across D55. ResistorR53 is to tie the base of transistor TR11 to its emitter when no driveis present.

Then transistor TR11 conducts, a voltage is developed across itscollector load R54, this voltage drives. transistor TR22 via resistorR81 and resistor R82 ties the base of transistor TR22 to its emitterwhen transistor TRl 1 is not conducting. When transistor TR22 conducts,relay RL4 its collector load is energized. Diode D39 prevents damage totransistor TR22 when a voltage is induced in the relay RL4 coil when thetransistor TR22 is turned off.

Contact RL9A energizes the down contactor, contact RL9D short circuitsR85 to give full drive to the thyristors. Contact RL9E ensures that thedrive to the thyristors is unaffected by speed, (i.e., no feedback).Contacts RL8B and RLSC ensure that the delay circuit operating RL3 isinoperative, and contact RL8A interlocks the hoist contactor A byopening thereby preventing feed to contactor B. Contacts RL9B and RL9Creverse the tachogenerator output polarity to enable the rotorcontactors to operate.

Relay RL8 when deenergized has a slight delay to enable the changeoverfrom power lowering to brake lowering to be carried out reasonablysmoothly when changing from notch RCLS to notch RCL4.

When lowering on notch RCLS the motor is conventionally powered, contactRCLS on the controller operating relays RL8 and RL9.

For hoisting and lowering on notch RCLS where a slip ring motor is used,the contactors .l, K and L (FIG. 1) are operated at the correct motorspeeds by the circuitry TR16, TR17 and relay RLS and associatedcomponents for contactor J, transistors TR18, TR19, and relay RL6 andassociated components for contactor K, transistors TR20, TR21 and relayRL7 and associated components for contactor L. These circuits are fedfrom the tachogenerator G, the output of which is fed to a potentialdivider, one for each contactor. R61 and R62 for contactor J, R67 andR68 for contactor K, R73 and R74 for contactor L (FIG. 2C).

When the voltage at the junction of the resistors R61-R62, R67-R68,R73-R74 exceeds the voltage rating of Zener diodes D42, D44 and D46, thetransistors TR16, TR18, TR will conduct and operate their respectiverelays RL5, RL6 and RL7, which in turn will operate their respectivecontacts J, K and L.

Capacitors C22, C23, C24, C25, C26 and C47 are to smooth out anyfluctuation in drive voltage, diodes D43, D45 and D47 protectstransistors TR17, TR19 and TR21 from damage resulting from the inductivekick when turning off similarly as for diode D39. Resistors R66, R72 andR78 are for bias purposes and rectifier D51 prevents reverse voltagefrom being applied when lowering at slow speed. As speed is reduced, thevoltage at the potential dividers R6l-R62, R67R68, R73-R74 will fallbelow the Zener voltage of diodes 42, 44, 46 and the transistors TR16,TR18, TR20 will stop conducting thereby releasing the relays RL5, RL6and RLK7 and eontactors J, K, and L.

Transistor TR23, Zener diode D54, relays RLl and RL2 and associatecircuitry ensure that, on lowering, if the maximum set overspeed isexceeded for any reason, the crane main contactor is deenergized, due toZener diode D54 conducting and energizing relay RL2 which deenergizesrelay RLl by short eircuiting the drive applied to transistor TR23through resistors R83 and R84 by means of contact RL2A.

This applies the brake and cuts off power to the motor until the resetbutton X is operated (FIG. 2A), diode D40 protects transistor TR23similarly as diode D39 protects transistor TR22.

The control of the firing angle of the thyristors is carried out by asawtooth voltage waveform derived from the phase to be controlled atterminals P, Q and R in FIG. 2A, the sawteeth are achieved by chargingfroma square wave of fixed amplitude via resistors R25, RVl and RV2 andcapacitors C6, C13 and C18, one for each phase. The square waves areobtained from the sinusoidal supply by Zener diodes D19, D29 and D34 inconjunction with the ballast resistors R10, R11, R12. The sawteeth areapplied to the bases of the transistors TR3, TR6 and TR9 via resistorsR24, R36 and R45 and speed up capacitors C7, C12 and C17 to improvewaveform front so that each will conduct when its sawteeth voltageexceeds that of the common emitter bias 100.

The output obtained across the collector loads R22, R34 and R43 oftransistors TR3, TR6 and TR9 are fed through resistors R21, R33 and R42,capacitors C5, C11 and C16 to drive transistors TR2, TRS and TR8 eachhaving a bias resistance R20, R32 and R41. When these transistorsconduct, an output voltage appears across the collector load resistorsR19, R31 and R100.

To vary the conduction angle, the bias is adjusted by a transistor(TR13, TR14, TRIS) controlled from the tachogenerator G.

Variable resistors RV1 and RV2 are to adjust the rated rise of thesawteeth so that all three phases are identical.

The discharge of capacitors C6, C13 and C18 is carried out by D16, D17,D18, R26 D26, D27, D28, R37 D31, D32, D33, R46 to ensure quick dischargeto a clamp voltage level supplied by resistors R14, R15 and decoupled bycapacitor C2.

For hoisting all loads and lowering light loads the bias 100 is set toapproximately zero so that the thyristors are turned on as soon as thesawtooth starts. This gives full power to the motor. When the set speedis attained, the transistors TR13 and TR14 start to conduct and raisethe bias level until just sufficient power is fed to the motor tomaintain the set speed. Any increase in speed will result in lower powerbeing fed to the motor and any decrease in speed will result inincreased power being fed to the motor to correct any deviation.

For lowering heavy to moderate loads, where the motor is used as abrake, the bias 100 is set to a level above the peak of the sawtooth sothat the load will descend under gravity until the set speed isattained. The transistor TR15 will thereby be caused to conduct by thetachogenerator and the bias 100 will reduce, thus causing the thyristorsto conduct and feed braking power into the motor. I

The operation of transistor TR13, TR14 and TR15 is as follows: when theselection hoist speed is attained the voltage applied to terminals 20and 47 fromthe tachogenerator exceeds the conducting voltage of theZener diode D48 causing transistor TR13, i.e. the emitter follower toconduct, the voltage across its emitter load R56 driving transistor TR14via resistor R55. The collector current of transistor TR14 flows throughthe circuit comprising resistor R57 and R60, the voltage across R60forming the emitter bias 100 for transistors TR3, TR6 and TR9. Thisvoltage causes TR3, TR6 and TR9 to start to turn off and reduce theconducting angle of the thyristors D1, D4 and D7 to reduce power to themotor F.

This also applies to lowering light loads after relay RL3 has operated.

When a moderate to heavy load is lowered the resistor R (FIG. 2A) is incircuit and the bias is such that transistors TR3, TR6 and TR9 are' off,and no power is fed to the motor (FIG. 2B). The load will descend undergravity until the selected speed is attained when the tachogeneratorvoltage applied to terminals 20 and 47 exceeds the conducting voltage ofZener diode D41 when transistor TR15 will start to conduct due to basedrive following through resistor R59 and reduce the bias untiltransistors TR3, TR6 and TR9 start to conduct to turn on the thyristorsD1, D4 and D7 and produce braking torque by means of the motor F.

Zener diodes D49 and D50D49 and D50 and ballast resistor R80 are toprotect transistors TR13 and TR15 from overvoltage when slow is selectedwhile in fast motion, the voltage then being high until the control hasreduced the speed. Capacitor C21 damps any possible oscillation of thebias 100 to which it is connected.

The hoisting and lowering speed selection notes, five for each directionare shown in FIG. 2A (RE/H1 to RE/HS for hoisting RC/LI to RC/L4 forlowering, RC/LS is full speed) which select the percentage of thetachogenerator voltage fed to the control unit C. Fine control of speedin by RV3-RV10. A rectifier selector, RC/H1-5 for hoisting, RC/Ll-S forlowering, which acts as a safety device is also shown.

The rectifier selected D52 or D53 in FIG. 2A is opposing the potentialof the tachogenerator output for the direction selected. Should alowering motion take place when on a hoisting notch, the rectifier D52will conduct and relay RL2 in FIG. 213 will operate, therebydeenergizing the contactor A and applying the brake D via contact RL2A,transistor TR23 and deenergizes relay RLl to open circuit the hoist maincontactor circuit. Similarly rectifier D53 will conduct and the samewill follow if the unit is hoisting when on a lowering notch.

To enable a standard unit to be capable of controlling the speeds ofmotors with varying numbers of poles resistors R86 and R87 are used sothat a constant full speed voltage is derived independent of the numberof motor poles and hence full speed r.p.m. decreased and a fullyvariable speed control is available, when the tapped resistor chainbecomes a single potentiometer.

The low voltage power for the transistors TR1-TR23 is obtained fromtransformer T1, FIG. 2A, connected to the supply via terminals L11 andL13 and fuses.

Two low voltage outputs are obtained from the transformer T1, eachconnected to a bridge rectifier D10-l3 and D20 23 to obtain DC voltage.

The voltage is stabilized by means of Zener diodes D14 and D24 and arefiltered by means of capacitors C1 and C8.

A contactor CF FlG. 2A is to enable the electromagnetic brake D todeenergize quickly, by breaking the DC connection and preventing thebrake holding off due to the inductive currents circulating through therectifier while the magnetic field collapses.

A travel motion which is similar to that of FIG. 2 may be employedhaving an A/C tachogenerator G1 and a current limiting transformer T4 asis shown in FIGS. 3-5. The transformer T4 (FIG. 4A) output which isrectified by the rectifier bridge D38-D4l and is fed to a load resistorRV51, a small load R36 is also present on the AC output in case of opencircuit in the rectifier D38D4l at some time.

The DC voltage across the load RV51 which is proportional to the AC loadcurrent passing through the primary of transformer T4 is connected tothe base of transistor TR12 via Zener diode D33, rectifier D32 andresistor R52.

Capacitor C23 smooths out any ripples in the rectified voltage when thevoltage at the wiper of resistor RV51 exceeds the Zener voltage of diodeD33, the transmitter TR12 will conduct, current will flow through itscollector load R43 and R42 to vary the bias 100 applied to the sawteethtransistors TR3, TR6 and TR9 and reduce the motor power.

The current at which this takes place is adjustable by means of thewiper on resistor RV51 and will control the motor acceleration andprotect the motor and equipment from over current.

- Control is similar to that-in FIG. 2 where TR13 and TR14 are now TR10,and TRll in H0. 4A.

R55, R56, R57, R60 are now R38, R39, R40 R41 and R42.

Since the output from the tachogenerator G1 is rectified to DC byrectifier D8, D10, D18, D20, D30, D31 the polarity is the same for bothdirections of travel, relays RLl and RL2 driven from the tachogeneratorvia transistors TR13 and TR enable the control unit to distinguish thedirection of travel. The relay RLl and RL2 depending on the directionselected, is energized by the controller contacts R or L terminals or 27(H6. 5) depending on whether right or left has been selected.

Once a direction has been selected and tachogenerator output obtained,the correct relay is energized, with contacts RLlB or RLZB indirectlymaintaining the relays RLl or RL2 by the rectified output from thetachogenerator until motion in that direction has almost ceased. ContactRLlA or RL2A ensures that no speed limitation is imposed if the selecteddirection is reversed, until after the motion passes through zero inorder to be able to reverse brake. Contacts RLlC and RL2C ensure thatwhen a direction has been selected and either RLl or RL2 energized, theother relay cannot operate until the first relay deenergizes when motionpasses through zero.

The transistors TR13 and TR14 which have the relays RLl and RL2 in theircollectors are driven from the rectified tacho output via ballastresistors R45 and R46 which in conjunction with Zener diodes D34, Dprevent damage to the transistors TR13 and TRl4 when full voltage isapplied. The drive to the bases of transistors TR13 and TR14 are takenfrom across the Zener diodes D34, D35 by resistors R47, R48, R49, R50.Diodes 36 and D37 prevent damage to the transistors on deenergization.

The relays controlling the direction of travel will operate at bridgeD56-D59,

a very small drive voltage from the tacho and will not deenergize evenwhen reverse direction is selected until motion in the originaldirection has ceased, the operation being similar to that for thelifting and hoisting control.

When open loop control is required the tachogenerator G relays RL] andRL2, transistors TR10 and TRll and associated components are omitted,and control is carried out with a variable resistor in place of TRll,the current limiting feature is retained.

What I claim is:

1. A control system for a reversible electric crane or hoist motorhaving a brake associated therewith, comprising an electrical supplysource; supply circuit means including motor reversing means, brakeactuating means, and thyristor means connecting said supply source tosaid motor; controller circuit means including a tachogenerator drivenby said motor, a static control circuit recervlng a feedback signal fromsaid tachogenerator and connected to and applying a control signal tosaid thyristor means for adjusting the firing angle of said thyristormeans in response to said feedback signal, thereby accurately andsmoothly controlling the speed of said motor; said controller circuitmeans also including hoisting and lowering contact means operable toactuate said motor reversing means to a hoisting or lowering positionand to actuate said brake actuating means to a brake release condition,and means associated with said static control circuit for permitting asufficiently heavy load to initially accelerate downwardly under gravityto a predetermined speed when said hoisting and lowering contact meanshas been set for lowering and for then causing said static controlcircuit to change the firing angle of said thyristor means to applycurrent to said motor in a hoisting direction, thereby applyingsufficient motor braking power to maintain said predetermined speed.

2. A control system as defined in claim 1, wherein, when said hoistingand lowering contact means is initially set for lowering, said motorreversing means is still positioned as for hoisting so that the load, ifsufficiently heavy, initially falls only under gravity until thepredetermined speed is reached at which time said thyristors means willpass current in a motor hoisting direction, thereby effectively applyingbraking power to said motor to maintain the predetermined speed.

3. A control system as defined in claim 2, said controller circuit meansincluding time delay circuit means operative after a period of time toautomatically actuate said motor reversing means to a lowering positionto effect lowering at said predetermined speed, thereby initiallypositively driving said motor in a lowering direction when the load istoo light to initially descend under gravity.

4. A control system as defined in claim 1, wherein said motor is a slipring motor in which the value of rotor resistance is controlled by themotor speed.

5. A control system as defined in claim 1, comprising means for stoppingsaid motor and applying said brake in the event said crane lowers whensaid controller has been set for he stmg.

1. A control system for a reversible electric crane or hoist motor having a brake associated therewith, comprising an electrical supply source; supply circuit means including motor reversing means, brake actuating means, and thyristor means connecting said supply source to said motor; controller circuit means including a tachogenerator driven by said motor, a static control circuit receiving a feedback signal from said tachogenerator and connected to and applying a control signal to said thyristor means for adjusting the firing angle of said thyristor means in response to said feedback signal, thereby accurately and smoothly controlling the speed of said motor; said controller circuit means also including hoisting and lowering contact means operable to actuate said motor reversing means to a hoisting or lowering position and to actuate said brake actuating means to a brake release condition, and means associated with said static control circuit for permitting a sufficiently heavy load to initially accelerate downwardly under gravity to a predetermined speed when said hoisting and lowering contact means has been set for lowering and for then causing said static control circuit to change the firing angle of said thyristor means to apply current to said motor in a hoisting direction, thereby applying sufficient motor braking power to maintain said predetermined speed.
 2. A control system as defined in claim 1, wherein, when said hoisting and lowering contact means is initially set for lowering, said motor reversing means is still positioned as for hoisting so that the load, if sufficiently heavy, initially falls only under gravity until the predetermined speed is reached at which time said thyristors means will pass current in a motor hoisting direction, thereby effectively applying braking power to said motor to maintain the predetermined speed.
 3. A control system as defined in claim 2, said controller circuit means including time delay circuit means operative after a period of time to automatically actuate said motor reversing means to a lowering position to effect lowering at said predetermined speed, thereby initially positively driving said motor in a lowering direction when the load is too light to initially descend under gravity.
 4. A control system as defined in claim 1, wherein said motor is a slip ring motor in which the value of rotor resistance is controlled by the motor speed.
 5. A control system as defined in claim 1, comprising means for stopping said motor and applying said brake in the event said crane lowers when said controller has been set for hoisting. 